1,3-butadiene (BD) is a known carcinogen. However, the DNA adducts responsible for mutations remain unknown. The overall goals of the proposed research are to examine the molecular dose of previously unexplored DNA adducts in rodents exposed to BD and 3-butene-1, 2-diol (BD-diol), comparing the data with mutation frequencies and mutational spectra to determine if a particular adduct could be used as a quantitative indicator of mutagenesis, and to evaluate effects of exposure on gene expression. The first hypothesis to be tested is that hydroxymethylvinyl ketone (HMVK) is formed in vivo during exposure to BD and BD-diol in a sex, species, and exposure concentration dependent manner resulting in important differences in mutagenicity. The second hypothesis is that promutagenic N1 adenine adducts convert to the more stable inosine adducts which are poorly repaired and accumulate during chronic exposure to BD. Several specific aims will be accomplished while addressing these hypotheses. Specific Aim 1 is to examine the formation of potentially mutagenic DNA adducts (specifically 1, N2-propanodeoxyguanosine) by HMVK in vivo. The second aim is to determine the utility of the N-terminal valine adduct of HMVK (HMVK-Val) as a biomarker of HMVK formation by BD and BD-diol. Specific Aim 3 is to develop methods for detecting N1- inosine, N1 - and N6 adenine adducts derived from BD metabolites in vivo. Specific Aim 4 is to determine the mutagenic responses induced by BD exposures and characterize the impact of BD-diol derived metabolites on the spectra of mutations induced by BD exposure in the B6C3F1 mouse and F344 rat to identify which adducts studied in Aims 1 and 3 are quantitative indicators of mutagenesis. Specific Aim 5 will examine the effects of exposure to BD and BD-diol on gene expression and DNA repair pathways. Collectively, these experiments have been designed to look at adduct formation, DNA repair, mutagenicity, and genomic alterations in rodents exposed BD and BD-diol, as well as the impact of glutathione depletion and DNA repair deficiency. Finally, HMVK-Val adducts will be measured in samples from BD exposed humans. Our research will identify critical metabolites and adducts that are responsible for BD mutagenicity, as well as develop biomarkers suitable for future molecular epidemiology studies. Ultimately these data will improve our understanding of critical mechanisms of toxicity and ability to accurately assess the risk of BD to humans.